Controlled emittance coatings for platinum-group metals

ABSTRACT

A platinum-group metal or alloy thereof having a controlled emittance coating comprised of an oxide of a metal selected from the group including manganese, nickel, chromium, iron and cobalt, the oxide being diffusion bonded to the metal. A method of applying a controlled emittance coating to the platinum-group metals and alloys thereof, the coating being applied as a metal, such as nickel, chromium, iron, manganese or cobalt, and then oxidized and diffusion bonding the oxide to the platinum-group metal or alloy thereof.

United States Patent David F. Carroll Hermosa Beach;

Jack L. Blumenthal, Los Angeles; John R. Ogren, La Palma, all of Calif.

Sept. 21, 1967 Oct. 26, 1971 TRW lnc.

Redondo Beach, Calif.

CONTROLLED EMITTANCE COATINGS FOR PLATINUM-GROUP METALS 9 Claims, 5 Drawing Figs.

US. Cl. l48/6.3, 29/194,29/19L2, 117/71, 1 17/217, 148/6. 5, 148/315, 176/82 Inventors Appl. No. Filed Patented Assignee Int. Cl C231 7/02 Field of Search 148/63, 6.35, 31.5; 117/227, 230, 231, 71, 217; 29/194,

3,615,886 References Cited UNITED STATES PATENTS 1,720,675 7/1929 Hertz Primary Examiner-Ralph S. Kendall Attorneys-Daniel T. Anderson, Alan D. Akerst and James V.

Tura

ABSTRACT: A platinum-group metal or alloy thereof having a controlled emittance coating comprised of an oxide of a metal selected from the group including manganese, nickel, chromium, iron and cobalt, the oxide being diffusion bonded to the metal.

A method of applying a controlled emittance coating to the to the platinum-group metalor alloy thereof.

PATENTEDnm 26 Ian 3,515,8

David F. Carroll Jock LBlumenfhol J oh n R. Ogren INVENTOR.

ATTORNEY BACKGROUND OF THE INVENTION Controlling the surface emittance of radioisotope containment vessels for aerospace applications has been a problem in the prior art. This problem has been particularly severe when viewed in the context of the Federal radioisotope safety requirements which demand that no release of the, radioactive contents be allowed under any conceivable situation; that is, both normal operation and all abnormal modes of operation including abort modes. The most probable abort situation involves exposure of a fueled vessel to terrestial gases, such as air or water vapor and carbon dioxide, at elevated temperatures up to 2500" F. for an extended period of time, measured in years. The survivability of the vessel in this situation depends strongly on the vessel surface temperature which can be lowered to an acceptable level by the use of controlled emittance coatings. Such coatings are provided by the present invention.

SUMMARY OF THE INVENTION The coatings, according to the invention, are thermally stable in oxidative environments and substantially reduce the surface temperature of a containment vessel to provide better vessel survivability by imparting to a capsule surface a high value of emittance. Because of the refractory nature of the coating, the surface emittance will not change with time.

The invention is comprised of the formation of stable oxides of manganese, chromium, iron, cobalt and nickel on a platinum-group metal or alloy substrate surface. The platinum-group metals are comprised of palladium, platinum, rhodium, iridium, osmium and ruthenium.

Accordingly, an object of this invention is to provide thermally stable surface preparations that maintain high emittances for radioisotope fuel capsules. Uses for this invention, however, are not limited to radioisotope fuel capsules but have utility in many high temperature range applications, for example, controlled emittance coatings for electronic components in radioisotope thermal generator systems, and rocket propulsion systems.

Still another object of the invention is to provide coatings for claddings of the platinum-group metals and alloys, the coatings comprising an oxide of a metal applied by plating, for example, and then oxidized and diffusion bonded to the platinum.

The coatings, according to the invention, provide distinct advantages over the state of the art surface preparations for radioisotope containment capsules. The new coatings are stable in oxidizing environments to 2500 F. whereas the prior coatings on radioisotope containment vessels were utilizable to only [900 F. The new coatings are chemically compatible to 2500 F. with a new class of oxidation resistant cladding materials, such as the platinum-group metals and alloys thereof. Further, the present coatings, when used in conjunction with the platinum-group metals and their alloys, offer a unique combination of improved oxidation resistance and high temperature emittance over the prior art nickel and cobalt based superalloys.

Further objects and advantages of the invention may be brought out in the following part of the specification wherein small details have been described for the competence of disclosure, without intending to limit the scope of the invention which is set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the accompanying drawings, which are for illustrative purposes,

FIG. 1 is an isometric view of a platinum plate having an oxide of a metal diffusion bonded thereon in accordance with the invention;

FIG. 2 is a magnified end view of a platinum plate having a nickel oxide diffusion bonded on two opposite sides thereof;

FIG. 3 is an end view of a platinum plate having chromium oxide diffusion bonded on both sides thereof;

FIG. 4 is a view of a rod of a platinumgroup metal having a metal oxide bonded thereon in accordance with the invention; and

FIG. 5 is an illustration of a tube of one of the platinumgroup metals having a metal oxide diffusion bonded on the inner and outer surfaces in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventive process is comprised of depositing a metal coating, such as manganese, iron, cobalt, nickel and chromium, on one of the platinum-group metals such as palladium, platinum, rhodium, iridium, osmium or ruthenium or alloys thereof. The metal coating can be deposited on a substrate of one of the platinum-group metals or alloys by electrolytic techniques, chemical vapor deposition, sputtering and flameor-plasma spraying techniques. After the coating has been applied to one and/or both sides of a substrate of a platinumgroup metal or alloy, the coating is oxidized in air and simul taneously heat treated to affect difi'usion bonding between the coating and the substrate in temperatures between 1500 F. and 2000 F. for approximately 1 hour. The diffusion bonding is, in effect, a bonding of a substantial number of atoms of the coating metal and of the platinum-group metal so as to provide a very durable adherence of the coating, and is distinct from a mechanical attachment of a coating to a metal.

Referring again to the drawings, there is shown in FIG. 1 a substrate in the form of a flat plate 10 of one of the platinumgroup metals, having diffusion bonded on one side 11 thereof an oxide 12 of one of the metals, such as manganese, iron, cobalt, nickel and chromium. The metal, such as nickel, was deposited upon the platinum-group metal by one of i the techniques indicated and then oxidized, also as indicated above. The diffusion bonding is shown by the irregular sur faces as at 13 where the two metals are joined together. This can generally be seen only through high magnifications.

In FIG. 2, there is shown a substrate 17 of platinum having diffusion bonded thereto, on two opposite sides an oxide 18 of nickel. The nickel was plated upon the platinum in a conventional manner and then heated in air for approximately I hour at between 1500 F. and 2000" F. so as to oxidize the nickel and so as to diffusion bond it with the platinum. The dark particles 19 in the nickel oxide coatings illustrate the oxidation and the small particles as 20 within the platinum are particles of nickel oxide which have formed in the platinum body as a result of the diffusion of nickel into platinum and subsequent oxidation of the nickel.

The drawing in FIG. 2 was made from a 200x photomicrograph. The thickness of the platinum 1'7, as used for cladding on radioisotope containment vessels, was in the range of between 0.030 inch and 0.040 inch and the thickness of the nickel as plated on the platinum was in the range of several Angstroms to several mils.

In FIG. 3, there is shown a platinum substrate 23 having a coating 24 of oxidized chromium on opposite sides thereof. The oxidation occurred at 2000 F. for one hour. The diffusion bonding which had occurred between the chromium and platinum had not caused the penetration of the chromium oxide into the platinum to the same extent as that indicated in FIG. 2 where there is substantial penetration of the nickel. The view in FIG. 3 was made from a 200 X photomicrograph.

In FIG. 4, there is shown a rod 29 containing, for example. palladium, platinum, rhodium, iridium, osmium, ruthenium or alloy of two or more platinum-group metals. Plated on the rod 29 is a coating 30 which may, for example, be an oxide of manganese, iron, cobalt, nickel or chromium. The metal, such as nickel, was first coated on the rod 29 and then oxidized as indicated above. Similarly, in FIG. 5, there is shown a tube 3] containing one of the platinum-group metals and having a coating 32 externally and a coating 33 internally of an oxide of one of the metals, such as manganese, iron, cobalt, nickel or chromium. Here again, the metal was deposited on the platinum-group tube 31 and then oxidized and diffusion bonded. The following examples illustrate ways of carrying The procedure for applying an oxidized nickel coating on platinum was as follows:

I. A thin sheet of platinum having a thickness of 0.005 inch was degreased in a solvent, such as ethyl alcohol, to remove any organic contaminants.

2. The sheets of platinum were rinsed in unheated water.

3. The platinum was cleaned anodically in an alkaline metal cleaner, such as Oakite 190 or Turco 8144-2.

4. The platinum was nickel plated, the thickness of the plate varying from several Angstroms to several mils.

5. The plated platinum was rinsed in unheated water.

6. The platinum was heated in air for one hour at 2000 F. to oxidize the nickel and to diffusion bond it to the platinum.

EXAMPLE II The procedure for applying an oxidized chromium coating on platinum was as follows:

1. The platinum was degreased to remove organic contaminants.

2. The platinum was rinsed in unheated water.

3. The platinum was cleaned anodically in an alkaline metal cleaner, such as Oakite 190 or Turco 8144-2.

4. The platinum was plated with chromium in a conventional chromium plating bath, the thickness of the chromium coating being in the range of several Angstroms to several mils.

5. The plated platinum was rinsed in cold water.

6. The plated platinum was heated in air for 1 hour at 2000 F. to oxidize the chromium and to diffusion bond the oxide to the platinum.

EXAMPLE Ill The following is a simplified process for applying a coating in accordance with the invention:

1. Degrease the metal containing one of the platinum-group metals to remove organic contaminants.

2. Coat the degreased metal with nickel, chromium, manganese, iron or cobalt by any conventional electrolytic, chemical vapor deposition, sputtering or flame (plasma) spraying technique, the thickness of the coating being in the range of several Angstroms to several mils.

3. Heat the coated metal for 1 hour at 2000 F. to oxidize the coating and to diffusion bond the coating to the platinumgroup metal.

Total hemispherical emittance measurements on platinum plate with a 0.001 inch coat of nickel and subsequently oxidized in accordance with EXAMPLE I showed an emittance increase from 0.2 for bare platinum to 0.7 for coated platinum when tested in the l600 F. to 2200 F. range. Similar results would be obtained from coating manganese, iron, cobalt and chromium.

Metallographic examinations of nickel-plated platinum heated for 2000 hours in air at 2000 F. showed internal oxidation of the platinum but this did not occur in the case of chromium-plated platinum. These results only suggest that in cases of some metal combinations, platinum-nickel being one, consideration must be given to the effect of possible interactions between the coating material and the substrate.

in order to properly declare the spirit of this invention, the following terms are defined:

Substrate: a material taken from the class of platinum-group metals and containing palladium, platinum, rhodium, iridium, osmium or ruthenium. Alloys of two or more of the platinumgroup metals are also included.

Coating metal: a material taken from the class of metals including manganese, iron, cobalt, nickel and chromium.

Emittance coating: an oxide of a metal taken from the foregoing class of coating metals.

From the description of the invention, it is apparent that the coating metals can be preferentially oxidized on the substrate to form an adherent, ductile and thermally stable high emittance coating; that the emittance will be substantially higher than that of the uncoated substrate metals; and that the emittance of the coating will not be impaired by prolonged exposure to high temperature oxidizing environments.

The invention and its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts of the invention without departing from the spirit and scope thereof or sacrificing its material advantages, the arrangement hereinbefore described as being merely by way of example. We do not wish to be restricted to the specific forms shown or uses mentioned except as defined by the accompanying claims, wherein various portions have been separated for clarity of reading and not for emphasis.

We claim:

1. A method of applying a controlled emittance coating to a substrate of one of the platinum-group metals consisting of platinum, palladium, rhodium, iridium, osmium, ruthenium and substrates of alloys consisting of the platinum-group metals, consisting essentially of a. cleaning the substrate;

b. coating at least one face of the substrate with a metal selected from the group consisting of nickel, manganese, chromium, iron, and cobalt; and

0. air oxidizing the coating metal.

2. The method according to claim 1 in which:

the coated metal is oxidized by heating it in air at temperatures of at least l500 F. for approximately I hour.

3. The method according to claim 1 in which the platinum group metal is cleaned by:

a. degreasing the substrate to remove organic contaminants;

b. rinsing the platinum-group metal in water; and

c. cleaning the platinum-group metal anodically in an alkaline metal cleaner.

4. The method according to claim 3 in which:

a. the metals are rinsed in water after coating; and

b. the coated metal is oxidized by heating in air for approximately 1 hour in temperatures of from l500 F. to 2000 F.

5. The method according to claim 4 in which:

the thickness of the coated metal is in the range of from several Angstroms to several mils.

6. A method of applying a controlled emittance coating to a substrate of one of the platinum group metals consisting of platinum, palladium, rhodium, iridium, osmium, ruthenium and substrates of alloys consisting of the platinum-group metals, consisting essentially of:

a. degreasing the substrate to remove organic contaminants;

b. coating at least one face of the substrate with a metal selected from the group consisting of nickel, chromium, iron, manganese, and cobalt,

c. said coating having a thickness of between several Angstroms and several mils; and

d. heating the coated metal in air for approximately 1 hour at temperatures in the range of approximately l500 F. to 2000 F.

7. A substrate of platinum-group metal having a controlled emittance coating, consisting essentially of:

a. said platinum-group metal being one selected from the group consisting of platinum, palladium, rhodium, iridium, osmium, ruthenium and substrates of alloys consisting of the platinum-group metals,

b. a coating on said platinum-group metal substrate of an oxide of a metal selected from the group consisting of manganese, nickel, chromium, iron and cobalt,

c. said oxide being diffusion bonded to said metal.

8. The invention according to claim 7 in which:

said coated metal has a hemispherical emittance of approximately 0.7 in the temperature range of 2000 F to 2200" F. 

2. The method according to claim 1 in which: the coated metal is oxidized by heating it in air at temperatures of at least 1500* F. for approximately 1 hour.
 3. The method according to claim 1 in which the platinum-group metal is cleaned by: a. degreasing the substrate to remove organic contaminants; b. rinsing the platinum-group metal in water; and c. cleaning the platinum-group metal anodically in an alkaline metal cleaner.
 4. The method according to claim 3 in which: a. the metals are rinsed in water after coating; and b. the coated metal is oxidized by heating in air for approximately 1 hour in temperatures of from 1500* F. to 2000* F.
 5. The method according to claim 4 in which: the thickness of the coated metal is in the range of from several Angstroms to several mils.
 6. A method of applying a controlled emittance coating to a substrate of one of the platinum group metals consisting of platinum, palladium, rhodium, iridium, osmium, ruthenium and substrates of alloys consisting of the platinum-group metals, consisting essentially of: a. degreasing the substrate to remove organic contaminants; b. coating at least one face of the substrate with a metal selected from the group consisting of nickel, chromium, iron, manganese, and cobalt, c. said coating having a thickness of between several Angstroms and several mils; and d. heating the coated metal in air for approximately 1 hour at temperatures in the range of approximately 1500* F. to 2000* F.
 7. A substrate of platinum-group metal having a controlled emittance coating, consisting essentially of: a. said platinum-group metal being one selected from the group consisting of platinum, palladium, rhodium, iridium, osmium, ruthenium and substrates of alloys consisting of the platinum-group metals, b. a coating on said platinum-group metal substrate of an oxide of a metal selected from the group consisting of manganese, nickel, chromium, iron and cobalt, c. said oxide being diffusion bonded to said metal.
 8. The invention according to claim 7 in which: the thickness of said oxide is the range of from several Angstroms to several mils.
 9. The invention according to claim 7 in which: said coated metal has a hemispherical emittance of approximately 0.7 in the temperature range of 2000* F. to 2200* F. 